Plant for automatic spray application of paint

ABSTRACT

In a plant for automatic spray application of paint through a spray nozzle ( 12 ), two parallel lines ( 9,10 ) each lead from an associated arrangement ( 1,2 ) for supplying paint to the spray nozzle. After paint has been fed through one of the lines to the spray nozzle followed by closing of a valve means ( 15,16 ) associated therewith for changing the arrangement ( 1, 2 ) supplying paint, a device ( 24 ) is adapted to feed such a volume of fluid into this line upstream of the valve means, with respect to the paint feeding direction, in the reverse direction so that the paint present in the line is pushed back into the arrangement without the fluid reaching it.

FIELD OF THE INVENTION

The present invention relates to a plant for automatic spray applicationof paint through a spray nozzle included therein, said plant comprisingat least two arrangements for providing paint for spray applicationconnected to the spray nozzle through first supply lines arranged inparallel to each other, means for feeding paint in the respective linefrom the respective arrangement to the spray nozzle as well as firstvalve means arranged in the respective line downstream of the feedingmeans with respect to the feeding direction and controllable to open andclose the fluid connection between respective arrangement and the spraynozzle so as to allow spraying of paint coming from one arrangement atthe time, as well as a method for automatic spray application of paint.

Such a plant may have different fields of use, but the use of such aplant for painting objects, such as car bodies, by a spray paintingrobot will hereinafter be mainly discussed for illuminating theinvention but not in any way restricting it.

A plant of this type having at least two mutually parallel lines is usedprimarily so as to reduce the time periods of inactivity when changingpaint or color by cleaning one of the lines and make it ready forfeeding any new paint it hasn't fed before, while the other of the linesfeeds a paint of a certain type to the spray nozzle, so that change ofarrangement, i.e. application of a paint of a new type, may take placerapidly.

The arrangements, which usually are constituted by color changingarrangements with a magazine of a series of different paints or colorsas well as solvents and valves and regulating means belonging thereto,are most often comparatively bulky and heavy and are bad suited to beplaced close to the spray nozzle, for example in the robot case, and forinstance when painting car bodies a move of the arrangement to theregion of the spray nozzle would mean that the robot couldn't come intoand paint the car body internally, so that the first line usually has aconsiderable length, which for example in the case of spray paintingrobots for painting vehicles may amount to some meters. When thearrangement providing paint to the spray nozzle is to be changed thepaint present in the first line in question is in these plants alreadyknown flushed out through the spray nozzle to the exterior and getscompletely lost. It is usually sprayed out by flushing the line by asolvent provided by the arrangement. The great length of the first linemeans that a not negligible volume of paint is lost in this way at eachchange, which over a longer period of time results in high costs.Furthermore, the paint sprayed out is bad for the environment and smearthe surroundings, so that, for example cabins in which painting takesplace have to be cleaned relatively frequently. It is not possible tosolve this problem with paint losses by spraying the paint out intocontainers instead, since an unacceptable large amount thereof would berequired and the paint is also degraded in the contact with air.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a plant of the typementioned in the introduction, which finds a remedy to theinconveniences mentioned above of conventional plants.

This object is according to the invention obtained by providing such aplant with a device adapted to, after feed of paint through a first lineto the spray nozzle followed by closing the associated valve means forchanging to another arrangement providing paint, at a location upstreamof the associated first valve means with respect to the spray feedingdirection into this first line feed such a volume of a fluid in thereverse direction with respect to the feed that the paint present inthis first line is pushed back into the arrangement without the latterbeing reached by the fluid.

By supplying a fluid to the first line in this way for pushing the paintpresent in the first line back all the paint pushed back, into thearrangement may be saved and used next time paint of that type is to besupplied to the spray nozzle through the arrangement. It is an importantcharacteristic of the invention that not that much fluid is fed into thefirst line that also this fluid reaches the arrangement, since thatwould unacceptably lower the quality of paint in the arrangement. Theplant according to the invention not only results in a considerablesaving of paint and therefore costs, but the minimal waste of paint isconsiderate of the environment and cleaning of possible cabins in whichthe spray application is carried out becomes almost superfluous.

According to a preferred embodiment of the invention the device hasmeans for dosing the fluid for feeding a predetermined volume thereofinto the first line in the reverse direction. Such a dosing means isadvantageous, since it is extremely important that the volume of fluidfed into the first line in the reverse direction is well adjusted, andthe obtaining this is facilitated by such a dosing means.

According to another preferred embodiment of the invention the dosingmeans is adapted to ensure feeding of a volume of fluid in the reversedirection of the first line substantially corresponding to the volume ofthis first line from the location of the inlet of the fluid into thisfirst line and to the associated arrangement. A minimum waste of paintis obtained by this design of the dosing means.

According to another preferred embodiment of the invention, the dosingmeans comprises means for adjusting the predetermined volume of fluidfed by the aforementioned means, which constitutes a simple and reliablerealization of the dosing means. It is underlined that “corresponding”is to be given a broad sense and means that the stroke volume is soselected that the fluid fed into the first line exactly manages to pushsubstantially all the paint present in the first line back into thearrangement in question without entering therein itself.

According to another preferred embodiment of the invention, the devicecomprises means adapted to feed the fluid into the first line with apressure exceeding the pressure of the paint present in the first line,the means for feeding the fluid comprises a piston cylinder actuated bya pressure medium on the first side of the piston so as to press a fluidlocated on the opposite side of the piston out of the cylinder, and thesurface for the action of the pressure medium upon the first side of thepiston exceeds the surface for the action of the piston upon the fluidon the other, second side of the piston for obtaining a pressureincrease between the pressure medium and the fluid. For example thecompressed air normally already available in an industrial building mayby this be used for feeding the fluid into the first line, which alsoconstitutes a further preferred embodiment of the invention.

According to another preferred embodiment of the invention, the deviceis adapted to feed a fluid in the form of an agent cleaning the firstline into the first line in the reverse direction thereof. This is veryadvantageous, since a flushing of the fluid back out of the first linewill then automatically result in a cleaning of the first line, which inany case is necessary before the first line may be filled again by paintof another type for spray application thereof.

According to another embodiment of the invention the device is adaptedto feed a solvent into the first line. A cleaning of such a first lineby a solvent is normally required, and by using a solvent for pushingthe paint back into the arrangement in this way the flushing of thesolvent out of the first line may in this way result in an automaticcleaning thereof.

According to another embodiment of the invention the arrangements arecolor changing arrangements, which constitutes a very preferredapplication of the plant according to the invention.

According to another embodiment of the invention the plant has a secondline connected to the first line through a second valve means and meansadapted to, after the pushing back, feed the fluid out of the first linein the ordinary feeding direction for the paint through the second line,a regulating means is adapted to then keep the first valve means closedand the second valve means open, and the regulating means is adapted toonly open the second valve means during the feeding of the fluid out ofthe first line. The fluid may by this be sprayed out of the first linewhile avoiding that it is emitted into the exterior through the spraynozzle.

According to another embodiment of the invention, which constitutes afurther development of the embodiment last mentioned, the plantcomprises a collecting vessel for the fluid, and the second linedischarges into the collecting vessel. The surrounding may by this bespared from the fluid, which is advantageous in the case of using forexample a solvent as fluid, and it is also possible to try to reuse thefluid.

According to another embodiment of the invention, which also constitutesa further development of the embodiment mentioned before the last one,the plant comprises means for conducting the fluid back from the secondline to means for feeding it back to one of the first lines when thearrangement providing the spray nozzle with paint is changed next time.Substantially the same fluid may by this be used all the time forpushing the paint back to the arrangements, which is particularlyadvantageous when this is constituted by a substance harmful to theenvironment and/or a substance of a non-neglectable cost, so that thisembodiment is very well suited when a solvent is used as the fluid.

The invention relates also to a method for automatic spray applicationof paint according to the appended independent method claim, and theadvantages of such a method appear clearly enough from the discussionabove of the plant according to the invention.

Further advantages and preferred features of the invention appear fromthe following description as well as the other dependent claims.

BRIEF DESCRIPTION OF THE DRAWING

With reference to the appended drawing, below follows a description of aplant and a method for spray application of paint according to apreferred embodiment of the invention cited as an example.

In the drawing:

The figure is a schematic diagram of a plant according to the preferredembodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The plant schematically illustrated in the figure for automatic sprayapplication of paint is advantageously, but not in any way necessarily,applied to a paint spraying robot for painting for example automobilebodies, and this particular use will be the basis of the descriptionfollowing below. The plant comprises in a way already known twoarrangements 1,2 for providing paint for spray application thereof, thearrangements being formed by so called color changing arrangementshaving a series of sources schematically indicated, such as 3-8, ofdifferent paint colors connected to a respective first line 9,10 throughvalves 11. The color changing arrangements may have a large number ofdifferent color sources, which is indicated by the break shown in therespective line. By opening one of the valves 11 the color desired in aparticular moment may in this way be supplied to the first line 9,10 inquestion.

The parallel first feeding lines 9,10 extends from the two paint orcolor changing arrangements 1,2 to a spray nozzle 12 for a sprayapplication of paint on an object. The plant comprises means 13,14arranged in each first line 9,10 for feeding paint in the respectiveline from the respective arrangement to the spray nozzle, in which thefeeding means are preferably adapted to establish a dosed feeding ofpaint to the spray nozzle with a uniform volume flow and are, for thesake for example, constituted by gear pumps. First valve means 15,16 arearranged in a respective first line downstream of the feeding means13,14 with respect to the feeding direction, and they are controllableto open and close the flow connection between the respective arrangementand the spray nozzle so as to allow spraying of paint coming from one ofthe arrangements 1,2 at the time. A valve 17 is also connected to thespray nozzle 12.

Each arrangement 1,2 also has a source 18 for a solvent and a bypassline 19 around each pump for enabling clean flushing of the first linesbefore the color change is carried out at the respective arrangement.The plant has also a second line 20, which is in common to the firstlines and connected thereto through a separate second valve means 21associated with each of the first lines through a branching 22 eachconnecting thereto. The second line 20 discharges into a collectingvessel 23.

The characteristics of the plant described so far are known from otherplants of this type. The two color changing arrangements 1,2 arenormally arranged at the base of the robot in question, since they arecomparatively bulky and heavy, and the lines 9,10 extend over aconsiderable distance in the robot arms to the spray nozzle 12 at thefree extremity of the last robot arm. This distance is formed by theaddition of the distances x and y shown in the figure and is typically6,000 mm. When using such plants already known paint is sprayed from onearrangement at the time, and when it is changed from for example thearrangement 1 to the arrangement 2 either all paint is sprayed out ofthe line 9 through the nozzle 12 or it is sprayed to a vessel anddisposed of, after which a solvent from the solvent source 18 is flushedthrough the line 9 around the pump 13 through the bypass line and outinto the vessel 23 through the second line 20, while the valve means 15is closed and the valve means 21 is open, both belonging to the upperbranching 22 as seen in figure. This is carried out while the secondarrangement 2 provides the spray nozzle 12 with paint, so that thearrangement 1 with the line 9 is ready to provide the spray nozzle witha new color when so required, so that it may be rapidly changed betweenpaints of different colors. Thus, about 120 ml color or paint istypically lost at each color change in such a plant already known, whichmeans a considerable cost per year, since about 200,000 color changestypically takes place during each year in such a spray painting robot.

The new and characteristic features of the plant according to theinvention will now be described. The plant comprises a device 24adapted, after paint has been fed through one of the first lines to thespray nozzle followed by closing the valve means 15,16 associatedtherewith for changing arrangement providing paint in this first line ata location 25,26 upstream of the associated first valve means 15,16 withrespect to the paint feeding direction, to feed such a volume of a fluidtherein in the reverse direction with respect to the paint feeding thatthe paint present in this first line is pushed back into the arrangement1,2 without the fluid reaching it. The device has for this sake a thirdline 27, which leads to locations 25,26 of the first lines for feedingfluid thereinto through two branchings 28,29 and a respective thirdvalve means 30,31. Regulating means (not shown) are adapted to open thethird valve means when fluid is fed into the first line and otherwisekeep it closed. The third line 27 is connected to the outlet 32 of apiston cylinder 33 adapted to cause a dosed feeding of a fluid out intothe third line 27 for feeding a determined volume of fluid into therespective first line 9,10. The piston 34 of the cylinder has a firstside thereof connected to a pressure medium, preferably compressed airfrom the ordinary compressed air system 35 of an industrial building.This pressure medium is intended to act upon the surface of the pistonat first side 36, in which the surface is larger than the surface actingagainst the fluid at a second side 37 of the piston. so that a pressureincrease is obtained from the pressure medium to the fluid. The fluidpumped in this way out of the piston cylinder 33 is preferably asolvent, which the piston cylinder 33 may receive at an inlet 38 thereoffrom a distillation apparatus 39 connected to the collecting vessel 23.The piston cylinder 33 is also provided with a set screw 40 foradjusting the predetermined volume of fluid fed by the piston cylinderthrough adjustment of the stroke volume of the piston cylinder.

The function of the plant according to the invention is as follows. Thespray nozzle 12 sprays paint from the arrangement 1, in which the valvein the bypass line 19, the valve 30, the valve 16 and at least the valve21 in the branching 22 connected to the first line 9 have been closed.When a color change is to take place through changing to paint feedingfrom the arrangement 2, the following is made with respect to thearrangement 1 and the line 9 thereof. The first valve means 15 isclosed, the third valve means 30 is opened and the valve means of thebypass line 19 is opened. The dosing means 33 is after that actuated tofeed a predetermined volume of fluid, there in the form of a solvent,through the line 27 into the first line 9 at the location 25 in thereverse direction thereof for pushing the paint in the line 9 back andinto the color source of the arrangement 1 belonging thereto. Apredetermined volume of solvent is selected so that this does not enterinto the color source of the arrangement, but preferably so that itpushes substantially all paint present in the line 9 back into thearrangement 1. The solvent present in the line may after that be flushedthrough the line 9 and out into the second line 20, in which first thethird valve means 30 has been closed and the respective second valvemeans 21 has been opened before. This is advantageously taken place bysupplying any additional solvent from the solvent source 18. The fluidis also utilized for flushing the line 9 clean, so that this gets readyto receive another paint from the arrangement 1 when desired. Thesolvent reaches the collecting vessel 23 through the second line 20 andis then conducted further to the distillation apparatus 39 for removingpaint residuals and the like so as to after that be supplied to thedosing means 33.

The invention is of course not in any way restricted to the preferredembodiment described above, but many possible further modificationsthereof would be apparent to a person with ordinary skill in the art,without departing from the basic idea of the invention,

Fluid other than a solvent could for example be used for pushing thepaint back into the respective arrangement, but it is important that thefluid in question not destroy the paint. When using a water solublepaint, water could, for example, be used as the only fluid. However, itis advantageous to use a fluid that may also be used for flushing thefirst line clean.

The number of arrangements for providing color could of course be morethan two, although it will probably be enough to have two sucharrangements to avoiding unnecessary time periods of inactivity whenchanging paint.

The definition “means for feeding paint in the respective line from therespective arrangement” in the claims is to be given a broad sense andcomprises also the case of such a means being constituted by any paintpropellant means arranged at the respective arrangement. The feedingmeans could also be formed by other types of pumps, which could make thebypass lines shown superfluous.

“First supply lines arranged in parallel to each other” means that theyare connected in parallel, but they do not have to extend in parallel toeach other.

What is claimed is:
 1. A plant for automatic spray application of paintthrough a spray nozzle included therein, said plant comprising: at leasttwo arrangements for providing paint for spray application connected tothe spray nozzle through first supply lines arranged in parallel to eachother, means for feeding paint in the respective first line from therespective arrangement to the spray nozzle, first valve means arrangedin the respective line downstream of the feeding means with respect tothe feeding direction and controllable to open and close the fluidconnection between the respective arrangement and the spray nozzle so asto allow spraying of paint coming from one arrangement at the time, adevice adapted to, after feed of paint through one of said first linesto the spray nozzle followed by closing the associated valve means forchanging to another arrangement providing paint, feed into said onefirst line at a location upstream of the associated first valve meanswith respect to the feeding direction such a volume of a fluid in thereverse direction with respect to said feeding direction that paintpresent in this first line is pushed back into the associatedarrangement without the latter being reached by said fluid.
 2. A plantaccording to claim 1, wherein said device has means for dosing saidfluid for feeding a predetermined volume thereof into the first line inthe reverse direction.
 3. A plant according to claim 2, wherein thedosing means is adapted to ensure feeding of a volume of fluid in thereverse direction of the first line substantially corresponding to thevolume of this first line from the location of the inlet of the fluidinto this first line to the associated arrangement.
 4. A plant accordingto claim 2, wherein said dosing means comprises a piston cylinder havinga predetermined stroke volume corresponding to the volume of fluid to befed into the first line in the reverse direction.
 5. A plant accordingto claim 2, wherein the device comprises means for adjusting saidpredetermined volume of fluid fed by said dosing means.
 6. A plantaccording to claim 1, wherein the device comprises dosing means adaptedto feed the fluid into the first line with a pressure exceeding thepressure of the paint present in this first line.
 7. A plant accordingto claim 6, wherein said dosing means for feeding the fluid comprises apiston cylinder actuated by a pressure medium on the first side of thepiston so as to press a fluid located on the opposite side of the pistonout of the cylinder, and that the surface for the action of the pressuremedium upon the first side of the piston exceeds the surface for theaction of the piston upon the fluid on the other, second side of thepiston for obtaining a pressure increase between the pressure medium andthe fluid.
 8. A plant according to claim 1, further comprising acompressed-air-operated cylinder adapted to press said fluid into thefirst line in the reverse direction thereof.
 9. A plant according toclaim 1, wherein the device is adapted to feed a fluid in the form of anagent for cleaning the first line into the first line in said reversedirection.
 10. A plant according to claim 9, wherein the device isadapted to feed a solvent into the first line.
 11. A plant according toclaim 1, wherein said arrangements are color changing arrangements. 12.A plant according to claim 1, wherein the plant has a second lineconnected to the first line through a second valve means and meansadapted to, after said pushing back, feed the fluid out of the firstline in the ordinary feeding direction for the paint through said secondline, wherein a regulating means is adapted to then keep the first valvemeans closed and the second valve means open, and wherein the regulatingmeans is adapted to only open the second valve means during such feedingof the fluid out of the first line.
 13. A plant according to claim 12,wherein said second line is in common to the first lines, and that aseparate second valve means is associated with each of the first linesthrough a branching from the second line connected thereto.
 14. A plantaccording to claim 12, further comprising a collecting vessel for saidfluid, and that said second line discharges into the collecting vessel.15. A plant according to claim 12, further comprising means forconducting the fluid back from said second line to means for feeding itback to one of the first lines when the arrangement providing the spraynozzle with paint is changed next time.
 16. A plant according to claim1, further comprising a third valve means arranged in a line for supplyof fluid to the respective first line, and that regulating means arearranged to open said third valve means when fluid is fed into the firstline and otherwise keep it closed.
 17. A plant according to claim 1,wherein one of said feeding means is arranged in each of the first linesand adapted to establish dosed feeding of paint to the spray nozzle at auniform volume flow in spray application of the paint from therespective arrangement.
 18. A method for automatic spray application ofpaint through a spray nozzle, said method comprising selectively feedingpaint to a spray nozzle from one of at least two arrangements forproviding paint for spray application by the spray nozzle, so thatspraying of paint from one arrangement at the time is made possible,wherein after feeding paint from one arrangement in a first line to thespray nozzle, when a change is carried out for feeding paint from theother arrangement, the first line is cut-off and a fluid is fed intothis line upstream of the location for the cutoff with respect to thedirection of said feeding of paint to the spray nozzle, said fluid beingfed in the reverse direction with respect to said feeding of paint atsuch a volume that the paint present in the first line is pushed backinto said arrangement without allowing said fluid to reach it.